[feature request]: Support rendering LaTeX math expressions in documentation comments

[dzylikecode]

It would be useful if Dart documentation comments could render mathematical expressions written in LaTeX syntax.

Dart documentation comments already support Markdown, but currently there is no built-in way to render mathematical formulas in generated API documentation.

For example, it would be nice to write:

/// Computes the loss function:
///
/// $$
/// L(\theta) = \frac{1}{N}\sum_{i=1}^{N}
/// (f_\theta(x_i) - y_i)^2
/// $$
///
/// The gradient is $\nabla_\theta L(\theta)$.
double loss(...) {
  ...
}

and have dart doc render both the block and inline equations as formatted mathematics.

[srawlins]

GitHub supports a syntax that uses MathJax I believe. https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/writing-mathematical-expressions

This sentence uses $` and `$ delimiters to show math inline: $\sqrt{3x-1}+(1+x)^2$

So if it were well-specified in GFM (which I do not think it is), we could add it easily. Otherwise it is sort of a product decision whether we depart from GFM, but align with what users will see on GitHub in their READMEs and other Markdown files.